Katie Crosier certainly does not look like the Seabrook Slasher. She is blond and billowy, prim and prancy. She wears pink toe-nail polish that matches her lipstick, and an ankle bracelet that reads "K-A-T-I-E." At 18, she's the kind of attractive that only those well beyond 18 can officially appreciate.

But slasher, crasher, masher - any is a more apt description of Katie Crosier and the thing she does best. She is a national and international judo champion, the only one in the Washington area, male or female.

"I just enjoy beating people," says Crosier, asked for perhaps the trillionth time to explain her unusual pastime. "Not smashing their heads into the mat, no. I just like to win."

If males still lurk out there who would sneer, consider this: Katie Crosier regularly beats men in practice who are 50 pounds heavier. Repent, ye chauvinists, and retreat: This is some kind of tough cookie.

Crosier is also the possessor of a dream. The scene: Moscow. The year: 1980. The setting: an Olympic victory stand, on which she is perched, higher than the two other medal-winners in the 130-pound division. The music: But of course - The Star-Spangled Banner.

But Crosier's dream resides only in her head for the present, because judo is not yet an Olympic event, and shows little expectation of becoming one in time for the 1980 games.

Four years later may be another story, however. The 1984 games are likely to go to Los Angeles, and the host country can institute new events. Besides, Katie Crosier will be 25 then, generally acknowledged to be the peak age for female judoists.

For now, though, fantasy in gold gives way to sweat, grunge and exhaustion, three times a week, at practice in the Alexandria studio of James Takemori. There, Katie Crosier lives out the classic pattern of the amateur athlete - she does her thing strictly forthe love of it.

"Some days, I'm so tired, I could just drop dead," said Crosier. "But I guess I'm determined."

Indeed, How else to account for a young woman who admits she has dabbled in karate, swimming and baton twirling - but just to build up her judo?

How else to explain the daily jog through her hometown streets of Seabrook, Md., in everything from snow to air pollution? How else to explain Katie Crosier's victory at the age of 13 in an international women's tournament over a woman more than twice her age?

But why judo? Why not softball? Or, if you insist, wrestling? Or, if you will, the "combat" of male-female relations?

"Judo just holds so many more things than anything else," said Crosier. "It keeps my weight down. I get to travel. I've made so many frinds i'd hate to give up. Plus it's just great for nervous tension.

"I have had some problems with boys because of it. Guys think of judo as a killer sport. I think they feel threatened, amybe not physically, but ego-wise."

Crosier pauses and smiles. "I don't think I look like some big brute. I wear dresses, you know? And I don't want to be 35 and all alone.

"But no one ever helped me across the street."

Crosier fell upon judo - pun intended - at the same time her brother Kenny, 20, was winning state honors in wrestling. She said she has "never gotten anything but encouragement," especially from her parents, Charles, an FBI agent assigned to Hyattsville, and Jean, a librarian at the National Institutes of Health.

"My father's driven me to tournaments in Michigan, California, everywhere. A lot of fathers are real egomaniacs, but he's not.

"My mother pushes the competition a little less. You know, if you win, fine; if you don't, fine. She looks more at the good aspects of judo. I mean, it's kept me out of trouble."

On the mat, the Crosier style is much muscle and little finesse. Even though she has been a black belt, the highest rank in the sport, since last June, Crosier admits her technique "isn't even good." To improve it, and to prepare for next year's national championships (she was "only" third in this year's), are her immediate goals.

Training for Crosier is matwork and more matwork. "I seldom lift weights, and I like to work on special moves," she said.

Crosier also undergoes a constant battle, like that of a jockey, to keep her weight in check. To weigh more than 130, her normal total, would catapult her into a new and more menacing weight division. Crosier would just as soon hold firm at 129.

Her major regret, now that she has achieved championship status, is that amateur athletes in the U.S. are not "supported" the way they are in many other countries.

"Being an American, I'm thankful for the opportunity to do other things," Crosier said. "But in a lot of Communist countries, they take the athelets aside at an early age and pay their expenses. It's got to give them an advantage."

Her parents, Crosier said, have picked up all her expenses. It has often been a considerable sacrifice, always in terms of time, often in terms of cash-on-hand.

For Crosier herself, there are other sacrifices. A second-year student at Prince George's Community College, she acknowledges that juso practice can crimp her study time.

She also says that fellow students sometimes whisper about the "celebrity" in their midst. "I usually don't tell people (about her judo honors)," Corsier said. "My friends tell them."

But Crosier is determined that judo will be in her future.

Although she wants to be an FBI agent like her father some day, she also plans to become a judo coach. "I want to coach girls to be champions," says a woman who is one herself. "I would never be satisfied with just a small community club."

Judo, says Katie Crosier, "is obviously a big part of my life, but it's not my whole life." Still, she adds, "my husband will probably be a jock, too." And which sport will he specialize in? It won't be polo, folks.